2 ways to change logos in Magento- Full Details

As you start to customize your newly installed Magento 1.6 webstore, you'll probably want to change the logo that displays in the top right section of the header on each page. This can be easily accomplished in the Magento 1.6 Admin Panel at any time.

Frist way
Uploading your logo to Magento
In Magento 1.6, to change the logo you simply have to specify a new URL path to the logo. If you want to place the logo in the same folder as the default one, you'll have to use cPanel's File Manager or FTP.

Read Details: http://forum.cmsideas.net/threads/2-...in-magento.89/

Open Magento admin panel and navigate to the Stores -> Configuration -> Design -> Header tab. Click on the Choose File button next to the Logo Image, select an image from your PC and save changes by clicking the Save Config button on top right. Refresh the website to see the new logo.